1. Field of the Invention
The present invention relates to a method of producing a thin-film system by plasma-aided chemical or physical vapor-phase deposition, containing at least one ultra-thin film. Such thin film systems are used in a wide variety of ways in technical applications, such as in the manufacture of magnetic and magneto-optical storage media, in the manufacture of cathode ray tubes and flat panel monitors with an electromagnetic radiation screen, and for high-performance optical and laser-optic beam splitters. However, these are non-limiting examples, and the invention is not restricted to these examples.
2. Discussion of Background Information
Numerous thin-film systems for optical, electrical and magnetic applications include ultra-thin films in the thickness range from 1 to 10 nm. These act as a barrier against solid or gas diffusion, as a nucleation film to influence the growth and crystal size of the subsequently applied film, and in many other ways. Since the properties of these ultra-thin films are usually also decisive in determining the properties of the overall film system, and indeed enable certain parameters to be met in the first place, high demands are frequently placed on such ultra-thin films. They relate to precise conformance to the specified film thickness and its homogeneity across the entire substrate, a high optical transparency in the case of optical functional film systems or a specific grain size and/or texture of film systems for magnetic or magneto-optical storage media, as well as a high degree of reproducibility of the properties cited.
Optical film systems with high transparency in the visible spectral range and high reflectance in the close infrared range are known, such as disclosed in EP 0 104 870 A1 and its U.S. family member U.S. Pat. No. 4,462,883, which are incorporated by reference herein in their entireties, which, in addition to tin oxide and silver films, also contain an ultra-thin copper film.
A method of producing low-resistance transparent electrodes from indium/tin oxide is also known, such as disclosed in A. Klxc3x6ppel et al., Thin Solid Films 365 (2000) 139-146, which is incorporated by reference herein in it entirety, by which a substantial reduction in surface resistance can be achieved based on an ultra-thin silver film with enhanced electrical and optical properties.
Numerous proposals for increasing the recording density of magnetic hard disks are known, based on the introduction of multiple film systems with ultra-thin intermediate films and/or nucleation films, such as disclosed in U.S. Pat. Nos. 5,846,648, 5,922,442, and Jie Zou et al. IEEE Transactions on Magnetics, Vol. 34 No. 4 (1998), 1582-1584, each of which is incorporated by reference herein in its entirety. Such thin-film systems generally also contain much thicker functional films, which have to be produced in sequence with the ultra-thin films. The methods of depositing such multiple film systems are frequently implemented in so-called short-cycle vacuum charging plants, using plasma-CVD or plasma-PVD processes. A set time is allotted for the manufacture of each individual film in the film system, and the film deposition is effected with a stationary substrate. The shortest possible cycle time is produced from the thickness of the thickest film and the deposition rate at which it is deposited. The plasma-aided chemical vapor deposition (CVD) and physical vapor deposition (PVD) methods applied usually use magnetron discharges.
The extreme thinness of the film means it is necessary to select a short coating time and/or a very low deposition rate in plasma-aided deposition of the film. Very short coating times make precise setting of the film thickness more difficult. If the coating time is dictated by other process steps, the only remaining technique of obtaining ultra-thin films is to reduce the deposition rate. If the deposition rate is set by variation of the power output of a magnetron discharge, below a certain minimum power output dependent on the size of the magnetrons it is no longer possible to ensure the uniformity of the physical properties of the ultra-thin film referred to the area of the substrate. Furthermore, the low power density required in such a case for a low deposition rate means that in plasma-aided deposition of the film the reproducibility of the film properties is significantly lower than that of comparatively thicker films deposited at a higher deposition rate and plasma power density.
The reasons for the difficulties cited, which are detrimental to a number of different film properties, obviously lie in a time and space non-uniformity of the plasma during film deposition, which occurs at low power densities in the plasma in particular. This applies especially to deposition methods which use magnetron discharges, e.g., magnetron atomization.
DE 198 55 454 and its U.S. family member U.S. Pat. No. 6,150,015, which are incorporated by reference herein in their entireties, disclose a method of enclosing the space in which the film-forming particles are created with only reduced cross-section vapor outlet openings to the substrate, meaning that the flow of film-forming particles is restricted. In this way, a higher plasma density and a more uniform distribution of the plasma can be achieved at least in the environment in which the film-forming particles are created. Despite some improvements in the reproducibility of the film thickness, as well as the attained properties and the uniformity of the film, this method remains subject to a number of disadvantages.
In addition to the increased cost, the elements employed to restrict the particle flow also result in greater process uncertainty. The efficiency of the deposition method is very low, and some properties are still not attained to the desired extent. In particular, this method cannot be applied for stationary deposition where high demands are placed in terms of the quality and uniformity of the ultra-thin films.
The present invention relates to providing a method which enables production of thin-film systems containing ultra-thin single films, preferentially in the film thickness range from 1 to 10 nm, of which the structural properties represent an improvement to the state of the art, with greater uniformity over the entire coating range, and with enhanced reproducibility.
The present invention is directed to a process of producing a thin-film system containing at least one ultra-thin film, which is deposited by plasma chemical vapor deposition or plasma physical vapor deposition using magnetron discharges, comprising depositing the ultra-thin film by introducing power output into plasma of the plasma chemical vapor deposition or plasma physical vapor deposition in the form of a controlled number of power pulses, and the average power output per unit time during pulse-on time is higher by a factor of at least 3 as compared to a total power output over a total coating time during deposition of the ultra-thin film.
The at least one ultra-thin film can have a film thickness of from 1 to 10 nm.
The average power output per unit time during pulse-on time can be higher by a factor of at least 10, or a factor of at least 20, and even a factor of at least 30 or higher, as compared to a total power output over a total coating time during deposition of the ultra-thin film.
The power output can be fed periodically or aperiodically into the plasma in a form of power pulses.
The process can include introducing 100 to 10,000 power pulses to obtain an entire deposition of the ultra-thin film.
At least one of power density and pulse duration of the power pulses can be freely selectable.
The power density and pulse duration of the power pulses during deposition of the ultra-thin film can be kept constant.
During deposition of the ultra-thin film, the power pulses can be counted, the film thickness can be measured at least once after introduction of a specific number of power pulses, and a remaining number of power pulses required to attain the target film thickness can be calculated therefrom and pre-set.
The power output in each pulse can be essentially constant over time.
The power output in each pulse can rise over time.
The power output in each pulse can fall over time.
The present invention is also directed to magnetic film systems produced in accordance with the process of the invention.